In recent years, the internal circuit pattern has become finer with an increase in the packing density of an LSI. As the pattern becomes finer, wiring resistance increases due to a decrease in the cross-sectional area of a wiring and the capacity between wirings increases since a space between adjacent wirings becomes narrow.
As a result, wiring delay time to be dermined by wiring resistance and wiring capacity increases, and a further increase in the speed of an LSI becomes difficult. Moreover, with the advancement of the multi-core technology of the inside of an LSI and the three-dimensional integration technology of memory, the large-capacity signal transmission between cores and between a core and memory are necessary, and the signal transmission speed by electricity is a bottleneck of an increase in the performance of an LSI.
As a technology for solving such a problem of wiring delay incident to an increase in the packing density of an LSI, an optical interconnect technology that replaces an electrical signal with an optical signal is being focused. The optical interconnect technology is a system that transmits a signal by using an optical waveguide instead of a metal interconnect, and there is no increase in wiring resistance and capacity between wirings caused by the finer pattern similar to the above, and it is possible to expect a further increase in the speed of operation.
In the optical interconnect technology, with regard to a semiconductor laser used as a light source, the size of the device used in known optical communication is several μm in width and 100 μm in length, and is very large compared with a transistor and a wiring pitch of an LSI. Therefore, it becomes a big inhibiting factor against replacing electric interconnects with optical interconnects.
Hence, a micro-ring laser using a micro-ring resonator as a small-sized light source has been devised. An optical device needs to be integrated in an LSI for optical signal transmission between LSI chips, and small, simple and low-power semiconductor laser is being required, and a micro-ring laser is a very potent device. A micro-ring laser whose oscillation mode is so stable as to be capable of direct modulation has, in fact, not been realized.